Compositions for use in re-utilisable blasting apparatus



Nov. 6, 1956 J. F. WILLIAMSON 2,769,701

COMPOSITIONS FOR USE IN RE-U'IILISABLE BLASTING APPARATUS Filed Oct. 28, 1953 INVE N TOR John Epedenickwillimmsozg ATTORNEYS.

COMPOSITIONS FOR UE IN RE-UTILISABLE BLASTING APPARATUS John Frederick Williamson, Ardrossan, Scotland, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain Application October 28, 1953, Serial No. 388,841

Claims priority, application Great Britain December 5, 1952 6 Claims. (Cl. 52-14) The present invention relates to an improvement in the makeup of a blasting assembly suitable for use in fiery or gassy mines and of the kind wherein a charge of a solid composition capable of thermal decomposition with the evolution of gases without flame and capable of supporting its gas generating decomposition when initiated by heating applied to merely a local portion of the charge and a local heating means are enclosed in a pressure resisting container having a wall element adapted to yield under a predetermined pressure and allow the gases to vent into the bore hole through a ported venting head.

Considerable success has attendedthe use of a blasting assembly of the aforesaid kind wherein the thermally decomposable gas generating composition consists of a mixture of equimolecular proportions of ammonium chloride and sodium nitrite stabilised by the inclusion of a small proportion of anhydrous sodium carbonate or magnesium oxide. Compositions based on mixtures of ammonium chloride and sodium nitrite are capable when their decomposition is initiated by local heating to a moderately raised temperature of supporting their gas generating decomposition at a visible rate through the whole mass of the composition even at atmospheric pressure, and under the rising pressure conditions in the pressure resisting container this decomposition is sufiiciently accelerated to enable a charge of the composition in conjunction with an electrically actuated local heater to serve for blasting purposes in fiery or gassy mines.

Such thermally decomposable gas generating compositions, however, sufier from the following disadvantages. A large amount of fume is evolved due to unchanged ammonium chloride and this fume takes a long time to settle. About 50% of said composition must be converted into common salt as can be seen from theoretical considerations. This being so about 50% by weight of the compositions is wasted as gas evolving material. Furthermore, as these compositions continue to undergo decomposition at atmospheric pressure if initiated by local heating to a moderately raised temperature they will have a tendency to undergo decomposition at atmospheric pressure if accidentally ignited and such decomposition at atmospheric pressure leads to the production of oxides of nitrogen. Because self-sustained decomposition can take place at ordinary atmospheric pressure it is not permitted to'make up blasting assemblies down a mine, with for example a blackpowder igniter. The said compositions are also unstable if they become damp.

' The object of the present invention is to provide thermally decomposable gas generating compositions suitable for use in blasting assemblies of the aforesaid kind which will be free from the said disadvantages.

There is disclosed in United States Patent No. 2,046,- 194 inter alia a blasting device of the kind comprising a charge adapted on initiation to generate gas and a pressure resistant metal vessel containing the said charge together with suitable initiating means, the said vessel being adapted to release the generated gases at a sulficient preses atent sure to cause a blasting effect in the bore hole and the said charge being for example an aqueous solution of ammonium nitrate with or without other ammonium salts and/or urea. There are a number of disadvantages, however, in employing aqueous solutions containing ammonium nitrate. It would thus be highly desirable to produce solid compositions based on ammonium nitrate in admixture with metallic salts having combined water of crystallisation. Hydrated metal nitrates which give a low residue and a high water content are magnesium nitrate Mg(NO3)2.6H2O, calcium nitrate Ca(NO3)z.4HzO, aluminum nitrate Al(NO3)3.9HzO and ferric nitrate Fe(NO3)3.9H2O. Calcium nitrate, however, forms a highly hygroscopic eutectic liquid with ammonium nitrate, and ammonium nitrate ferric nitrate mixtures have bad storage properties.

According to the present invention a blasting device of the non-detonating gas generating kind in which a gas producing charge is confined within a pressure resisting shell having a member adapted to permit escape of the gases at a predetermined pressure and an electrically actuable chemical heating element capable of ignition and of generating a gas pressure in the free space in said container is characterised in that said gas producing charge consists of a pulverulent intimate admixture comprising ammonium nitrate, at least one of the hydrated nitrates of metals of low atomic weight of the group magnesium nitrate hexahydrate and aluminum nitrate nonahydrate, and a non-explosive organic fuel consisting substantially of a dried vegetable carbohydrate material, wherein the number of moles of combined water in the metal nitrate per mole of ammonium nitrate lies between 1 and 3 and wherein the proportion of the organic fuel in the pulverulent mixture is such that the gases from the charge and the heating element consist at the bursting pressure substantially of steam, carbon dioxide and nitrogen.

In calculating the required proportion of organic fuel in the mixture, allowance is made for the available oxygen requirements under the working conditions of any envelope that may be provided for such mixture and of any combustible parts of the chemical heating element and of the products which would normally furnish an actuation in a closed space.

The organic fuel in the admixture may consist for instance of woodflour, cereal meal, flours, and starches, and other finely divided forms of dried vegetable tissue material of carbohydrate character.

The preferred lower limit of the molar ratio of combined water in the hydrate used to ammonium nitrate in said admixture depends on the characteristics of the metal container, of the desired venting pressure and in an ordinary chemical type of pressure resisting container fitted with a disc yielding at 12 tons/ sq. in. it is preferred that this limit should not be less than approximately 1.4 moles combined water per mole ammonium nitrate. Care has to be taken to prevent damage to the tube due to possible violent decomposition of the ammonium nitrate.

The upper limit is imposed by the decreasing sensitiveness of the mixture to ignition making ignition unreliable.

Within the stated limit the more heat and gas pressure that are developed by a chemical heating element the higher may be the molar ratio of combined water to ammonium nitrate. When, as will usually be desirable, the chemical heating element is to be suitable for underground loading it must be incapable of producing a gas ignition itself, and in such instances it is desirable that the upper limit of the molar ratio of combined water to ammonium nitrate should not exceed about 2.5.

The electrically actuable chemical heating element enclosed with the charge in the blasting assembly must be capable of producing at least suflicient hot gas to raise the pressure within the pressure resisting container to 20 lbs./ sq. in. and preferably in excess of 8 atmospheres.

As an electrically actuable chemical heater suitable only for loading above ground there may be employed for instance an electric black'powder fuse. Where the container has a capacity of 680 cc. the b'lackpowder charge in this fuse may conveniently amount to about 4 grams in weight. As an electrically actuableelement capable of being loaded underground there may be employed for a container of this size a charge of 20 grams of a mixture of 8385% guanidine nitrate, 10l2% 2:4 dinitroresorcinol, the remainder of the composition being made up of mineral oil, vanadium pe-ntox-ide, potassium nitrate, triethanolamine, methyl ethyl cellulose and asbestos fibre in amounts not exceeding 1% of each of these ingredients, enclosed in a thin cardboard tube weighing 2 grams with an electric fusehead. An alternative composition consists of a charge of 20 grams of a mixture of 60% guanidine nitrate, 31 /2% potassium persulphate, 8% cuprous chloride and /2% mineral jelly enclosed with an electric fusehead in a thin cardboard tube weighing 2 grams.

The flarneless gas generating charges used in the blasting device of the present invention differ from charges based on mixtures of ammonium chloride and sodium nitrite in that they are incapable of sustaining their own thermal decomposition through a mass as the result of mere local heating of 'a portion thereof at atmospheric pressure so that even if a hot object should accident-ally come into contact with a portion of a charge in the mine at atmospheric pressure propagation of decomposition will not take place. and this fume is also less persistent than that obtained from compositions based on ammonium chloride and sodium nitrite. The gases are also satisfactorily free from poisonous or irritating constituents. The total amount of solid products formed is about one tenth the amount formed from ammonium chloride/ sodium nitrite compositions. The gaseous and solid materials projected are at too low a temperature to ignite fiery or dusty atmospheres or constitute any indirect ignition risk. The compositions used in the devices of the invention only undergo self-sustained thermal decomposition at pressures in excess of 20 lbs/sq. in. and preferably in excess of 8 atmospheres.

The charge of the invention can be used as a loose composition or packed in a suitable combustible container with the heating element inserted therein.

The invention is illustrated by the following examples and in so far as Examples 1 and 2 are concerned with reference to the diagrammatic drawing attached hereto.

Example 1 A pressure resisting steel container '1 is of 680 .cc.s capacity, of 1% inches internal diameter, and is provided with a disc 2 of inch thickness adapted to burst at 12 tons/ sq. in., a firing head 3 and a discharge head 4. The pulverulent composition 5 consists of a charge of 170 grams of a mixture of 49.2% magnesium nitrate hexahydrate, 38.8% ammonium nitrate and 12% woodfiour enclosed in a waxed paper wrapper 6 Weighing 20 grams and of external diameter /8 inch. The =loading density throughout the tube is 0.25. The electrically actuated heating element 7 embedded in the composition 5 is one containing a 20 gram charge of either of the two guanidine nitrate containing compositions hereinbefore referred to.

When the pressure resisting steel container 1 is loaded and utilised in the bore hole'in known manner the blast takes place with little fume and the fume evolved is relatively free from poisonous and irritating constituents. It is found that about half of the waxed paper wrapper 4 is oxidised. In this example only 14 grams of solid material are formed Whereas to obtain the same blasting eifect with an ammonium chloride and sodium nitrate In a blast less fume is produced 4 composition 280 grams are required and 140 grams of solid material are formed.

Example 2 v 64.5 grams of ammonium nitrate, 84 .grams of magnesium nitrate hexahydrate and 20.4 grams of woodfiour are intimately mixed and are contained in the form of a fine powder in a Waxed paper tube 6 of 20 grams weight. An igniter 7 consisting of an electrical fusehead and 20 grams of a gas producing composition (based on dinitroresorcinol and guanidine nitrate) in a paper wrapper weighing 2 grams is introduced into the centre of the paper tube 6. This composite charge gives a satisfactory result in the pressure resisting steel container 1 provided with a inch mild steel disc 2. The assembly 'vents satisfactorily after a delay of 2 seconds, and the amount of noxious gases produced is small.

Example 3 82.3 grams of ammonium nitrate, 56 grams of aluminum nitrate nonahydrate and 28.3 grams of starch are intimately mixed in the form of a fine powder. An igniter consisting of an electrical fusehead and 20 grams of a gas producing composition (based on d-initroresorcinol and g-uanidine nitrate) contained in a cardboard tube weighing 2 grams is used in conjunction with the loose powder charge in the pressure resisting steel tube of Example 1 provided with a %4.lllcl'l mild steel burst? ing disc. The assembly vents satisfactorily after a delay of 4 se'conds.

Example4 A charge of 130 grams consisting of 63.7 grams of ammonium nitrate, 44.2 grams of magnesium hexahydrate nitrate and 22.1 grams of starch intimately mixed and in the form of a fine powder is fired in the pressure resisting steel tube described in Example 1 with an electrical fusehead and Y20 grams of a gas producing composition .based on gu'anidine nitrate and potassium persulphate. The charge is insuflicient to produce the'pressure required to burst the inch mild steel disc so that the gas slowly escapes past the seating of the bursting disc. There is no evidence of any corrosion-of the steel tube and the residual liquid in the tube is slightly alkaline.

With a charge of 170,-grams of the aforesaid composition under the sameconditions of firing the assembly vents after a delay of 2 seconds. V t,

' Example 5 gives a satisfiactory result, the tube venting after a delay a of 1 second.

7 Example 6 A charge consisting-of an intimate admixture of 321.7 grams of magnesiuinnitrate hexahydrate, 248:3 grams of ammonium nitrate and 78.0 grams of woodfiour and V in a finely powdered condition is contained in a waxed cardboard tube: is introduced into a steel tube ,of 3 litres capacity together with grams of a gas producing firing composition based on potassium persulphate and guanidine nitrate. Theassembly gives a satisfactory result with a inch mild steel disc which ruptures after a delay of 7 seconds.

What I claim is: a a

l. A gas-producing charge suitable for use in association with an electrically actuable chemical heating element in a blasting device of the kind in which a gasproducing charge is confined within a pressure resisting shell having a member adapted to permit escape of the gases at a predetermined .pressure and an electrically and of generating a gas pressure in the free space in said container comprising a pulverulent intimate admixture comprising ammonium nitrate, at least one of the hydrated nitrates of metals of low atomic weight of the group magnesium nitrate hexahydrate and aluminum nitrate nonahydrate, and a non-explosive organic fuel consisting substantially of a dried vegetable carbohydrate material, wherein the number of moles of combined Water in the metal nitrate per mole of ammonium nitrate lies between 1 and 3 and wherein the proportion of the organic fuel in the pulverulent mixture is such that the gases from the charge and said heating element consist at the bursting pressure of said blasting device substantially of steam, carbon dioxide and nitrogen.

2. A gas-producing charge as claimed in claim 1 wherein the molar ratio of combined water in said hydrate to ammonium nitrate in the said admixture for a pressure resisting container fitted with a disc yielding at 12 tons/ sq. in., is not less than approximately 1.4 moles combined water per mole ammonium nitrate.

References Cited in the file of this patent UNITED STATES PATENTS 1,464,667 Snelling Aug. 14, 1923 2,048,827 Taylor July 28, 1936 2,154,221 Taylor Apr. 11, 1939 FOREIGN PATENTS 573,147 Great Britain Nov. 8, 1945 

1. A GAS-PRODUCING CHARGE SUITABLE FOR USE IN ASSOCIATION WITH AN ELECTRICALLY ACTUABLE CHEMICAL HEATING ELEMENT IN A BLASTING DEVICE OF THE KIND IN WHICH A GASPRODUCING CHARGE IS CONFINED WITHIN A PRESSURE RESISTING SHELL HAVING A MEMBER ADAPTED TO PERMIT ESCAPE OF THE GASES AT A PREDETERMINED PRESSURE AND AN ELECTRICALLY ACTUABLE CHEMICAL HEATING ELEMENT CAPABLE OF IGNITION AND OF GENERATING A GAS PRESSURE IN THE FREE SPACE IN SAID CONTAINER COMPRISING A PULVERULENT INTIMATE ADMIXTURE COMPRISING AMMONIUM NITRATE, AT LEAST ONE OF THE HYDRATED NITRATES OF METALS OF LOW ATOMIC WEIGHT OF THE GROUP MAGNESIUM NITRATE HEXAHYDRATE AND ALUMINUM NITRATE NONAHYDRATE, AND A NON-EXPLOSIVE ORGANIC FUEL CONSISTING SUBSTANTIALLY OF A DRIED VEGETABLE CARBOHYDRATE MATERIAL, WHEREIN THE NUMBER OF MOLES OF COMBINED WATER IN THE METAL NITRATE PER MOLE OF AMMONIUM NITRATE LIES BETWEEN 1 AND 3 AND WHEREIN THE PROPORTION OF THE ORGANIC FUEL IN THE PULVERULENT MIXTURE IS SUCH THAT THE GASES FROM THE CHARGE AND SAID HEATING ELEMENT CONSIST AT THE BURSTING PRESSURE OF SAID BLASTING DEVICE SUBSTANTIALLY OF STEAM, CARBON DIOXIDE AND NITROGEN. 